Infusion of fluids, such as drugs and plasma, into a patient is commonplace in the medical field. Two common infusion methods are intravenous delivery of fluids by gravity and either intravenous or intraarterial delivery by actually pumping the fluids for delivery to the patient.
In pump delivery, an infusion pump is used to pressurize the fluid. Past devices often require a complex cassette mechanism which comes into direct contact with the fluid to be delivered. Other devices require fluid to be fed by gravity to a pumping instrument having a cassette.
Peristaltic pumps acting upon in-line tubing segments have been used in this art. One example of a peristaltic pump, disclosed in U.S. Pat. No. 4,155,362, includes a back pressure valve to prevent gravity siphoning from the pumping chamber.
Another relatively simple pumping arrangement is disclosed in U.S. Pat. No. 4,142,524, in which a cassette is provided with inlet and outlet valves to and from a pumping chamber. The pump presses a rubber diaphragm on the cassette to diminish the volume of the cassette chamber by a known amount to deliver a predetermined quantity per pump stroke. An even simpler disposable element is disclosed in the pumping arrangement of U.S. Pat. No. 4,199,307, in which a pancake-shaped resilient pumping chamber is provided with upper and lower valves and an activating pumping piston which displaces a known volume on the pumping stroke. Yet another pump approach is disclosed in U.S. Pat. No. 4,322,201, which seeks to provide continuous, uninterrupted fluid flow by alternating between two pumping chambers, each of which employs the principle of the rolling diaphragm. A third rolling diaphragm chamber is employed for mechanically sensing pressure within the device for control purposes.
Another delivery pump system as disclosed in U.S. Pat. No. 4,657,490, employs a simple disposable element in combination with a relatively straightforward gravity supply and positive pumping action which is accurate and which provides pressure monitoring and self-checking diagnostics through measuring the pressure exerted on the pump actuator.
None of the foregoing art, however, provide a simple disposable element with a positive feed capable of drawing fluid from a negative head pressure supply in combination with simple straightforward delivery pumping action which is accurate and reliable and which provides improved reliability pressure monitoring through the cassette pumping membrane and self-check diagnostics.